{"id":49582,"date":"2020-11-05T00:05:02","date_gmt":"2020-11-05T00:05:02","guid":{"rendered":"\/forum\/forums\/topic\/unexpected-composition-fluctuations-in-a-directional-solidification-problem-with-species-transport\/"},"modified":"2020-11-05T00:05:02","modified_gmt":"2020-11-05T00:05:02","slug":"unexpected-composition-fluctuations-in-a-directional-solidification-problem-with-species-transport","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/unexpected-composition-fluctuations-in-a-directional-solidification-problem-with-species-transport\/","title":{"rendered":"Unexpected composition fluctuations in a directional solidification problem with species transport"},"content":{"rendered":"
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Dear Forum Members,<\/p>\n

I am setting up a model of directional solidification (crystal growth) with chemical species transport. The objective is to model solidification of an ingot and obtain a solute distribution profile in the final solid along the freezing direction. In the final model the convection in the melt will need to be included, however at this stage I am trying to debug the model that only accounts for Temperature, Solidification and Species with the momentum equations turned off.<\/p>\n

The situation that I am trying to replicate is a theoretical model of "Diffusion-Controlled 1-dimensional solidification" that occurs when a pool of molten material with evenly distributed solute is frozen by moving it with respect to a 1-D temperature gradient, without convection in the liquid phase (melt) and without diffusion in the solid phase (crystal or ingot). As the temperature decreases, the material starts to solidify at one end, and the solute is partially incorporated into the solid and partially rejected. This results in a solute concentration in the first bits in the solid lower than initial, and a build up of the concentration in the liquid next to the solid-liquid interface, due to limited solute transfer into the bulk liquid by diffusion. The build-up continues until the rate of the solute rejection at the interface is balanced by the rate of its transfer away by diffusion. In a final solid bar this process produces an "initial transient" of increasing concentration followed by a "steady-state" section, which is described by a picture below.<\/p>\n

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